Pattern inspection apparatus and electron beam apparatus

ABSTRACT

A pattern inspection apparatus is designed to quickly and accurately perform an inspection of an inspection sample, such as a mask or a wafer or the like by irradiating electron beams onto the inspection sample and detecting secondary or backscattered electrons reflected from the surface of the inspection sample and/or transmitted electrons passing through the inspection sample. The pattern inspection apparatus includes an electron beam generator including at least one electron gun for generating at least one electron beam irradiating onto the surface of the inspection sample. A movable support is provided for supporting the inspection sample. The apparatus also includes a detector unit having a plurality of electron detecting elements for detecting electrons containing information related to the construction of the inspection sample and a detection signal processor for processing simultaneously or in parallel formation the outputs of the electron detecting elements of the detector. Also, when a plurality of electron beams are used for simultaneous irradiation of the inspection sample, the pattern inspection apparatus includes a mechanism for avoiding interference between the reflected electrons of the adjacent electron beams.

This application is a continuation of application Ser. No. 08/190,575,filed Feb. 2, 1994, now abandoned which is a continuation of applicationSer. No. 07/975,368, filed Nov. 16, 1993, now abandoned and which is acontinuation of abandoned Ser. No. 897,451, filed Jun. 10, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pattern inspection apparatus. Morespecifically, the invention relates to a pattern inspection apparatusfor performing an inspection of a mask pattern, such as a mask, reticuleor the like to be used in exposure technology for transferring a finecircuit pattern onto a semiconductor substrate or of a fine circuitpattern formed on a wafer. More specifically, the invention relates to apattern inspection apparatus for inspecting a pattern configuration or adefect or an error in a pattern configuration of an inspection sample,such as a mask to be used for X-ray exposure technology for transferringa fine circuit pattern or the like onto a semiconductor substrateemploying an X-ray beam including a synchrotron radiation beam (SOR), awafer including a fine circuit pattern formed on a semiconductorsubstrate or a mask, reticule or the like to be used in light exposuretechnology for transferring a fine circuit pattern to a semiconductorsubstrate employing an ultra-violet light source.

2. Description of the Related Art

Conventionally, in order to transfer a fine circuit pattern onto asemiconductor substrate, ultra-violet light is used as a light source.Normally, a mask containing patterns for several chips is employed toperform a transfer of a compressed pattern onto a large diameter waferby periodically shifting the transfer position on the wafer in astep-and-repeat manner. At the present time, for inspection of waferpatterns to detect foreign matter or defects on the mask pattern or todefect foreign matter on the wafer or the wafer pattern, an opticalmethod employing an optical micrograph is frequently used. However, asthe density of fine circuit patterns has become greater, it has becomenecessary to provide a light source with a shorter wave length foreffecting wafer pattern inspection. In a conventional light sourceemploying a conventional optical system, resolution cannot be improvedbecause of specific diffraction limits which make it difficult to detectsmall defects.

To solve such a problem, electron beam inspection technology has beendeveloped.

Thus, to facilitate the increasing density of circuit patterns, X-rayexposure technology employing an X-ray containing synchrotron radiationbeam (SOR) is regarded as one of the important next age transfertechnologies. Simultaneously, it is becoming necessary to shorten thewavelength of the light source used for inspection of X-ray masks.

In the prior art, the object of the inspection is to determine thepresence of foreign matter adhering on the surface of the mask,reticule, wafer or the like, or to locate defects in a pattern such asthe protrusion 201, intrusion 202, break 203, bridge contact 204, pinspot 205 or pin hole 206 or the like as shown in FIG. 18. The generallyrequired sensitivity is, for example, in the case of foreign matter,

for a bare wafer: (pattern dimension)×1/7 to 1/5

for a patterned wafer: (pattern dimension)×1

for a reticule or mask: transfer limit.

On the other hand, in the case of a pattern defect, the requiredsensitivity level is generally (line width)×1/2.

With increased pattern and package density, higher sensitivity becomesnecessary. However, in the case of an inspection process employing alight beam, the extent to which the size of a light beam may be reducedis limited. Even when the wavelength is shortened, the highest possiblesensitivity of visual light is 0.25 μm. Therefore, the size of thedevice to be inspected is limited to 4M to 16M DRAM. On the other hand,even when an ultra-violet light beam is employed, the maximum possiblesensitivity to be achieved is 0.15 μm. In this case, the size of thedevice to be inspected can be up to 64M DRAM. Therefore, it is difficultto effect an inspection of a 256M DRAM or a next age device havingfurther reduced size and greater packing density, such as a 1G DRAM.

Therefore, a method employing an electron beam in place of the lightbeam has been considered.

In methods employing electron beams, fewer problems will result fromincreasing the pattern density and thus higher density patterns can beachieved than with a light beam.

However, in prior art electron beam processes, there is a problem inthat the information detected by a detecting means is processedindependently in a time sequence in a detecting process and therefore, arelatively long data processing period is required.

In addition, as set forth above, when circuit pattern and packagedensity are increased, the amount of data to be processed during patterninspection of the device is naturally increased. Therefore, it isrequired to provide a greater capacity for accepting data to bearithmetically processed.

For example, there is a tendency to require a process for (1 cm/0.1 um)²=100M pixel/cm², 8" wafer, 31G pixel/wafer.

In contrast, when the density of the circuit pattern is increased, thesize of the pattern unit for processing to check whether a defect ispresent or not becomes small. In addition, the capacity of theindividual chip is increased. Therefore, where there is an increase incircuit pattern density, the amount of information to be processed forinspection rapidly increases. In conventional electron beam systems, asingle electron beam is scanned across the mask in order to detectgenerated secondary, backscattered or transmitted electrons. Therefore,the signal stream from the irradiating region of an electron beam havinghigh convergence for detecting very small defects, is generatedcontinuously in a time sequence. A long time period is thus required forthe transmission of the image information to a signal processing system.Therefore, even when the speed of the signal processing system isincreased, a long time period is still required for inspection.

In a pattern inspection process employing an electron beam, the electronbeam is irradiated onto an inspection sample, such as a mask or wafer orthe like and the beam is scanned across the sample in order to generatean electron flow at the irradiated portion and introduce such electronflow into an electron detecting portion. The electron flow introducedinto the detecting portion contains configuration information relatingto the pattern. The signal contained in the electron flow provides timesequential pattern information.

The electron flow to be introduced into the detecting portion from theirradiated portion of the inspection sample may include secondaryelectrons which vary in quantity as function of the direction ofincidence to the detecting portion depending upon the configuration ofthe inspection sample, backscattered electrons which vary in amountdepending upon the material and configuration of the inspection sampleor transmitted electrons which vary in amount depending upon the patternof the inspection sample when the latter is a thin film mask or an X-raymask or the like. From these respective electrons, the planeconfiguration and three dimensional configuration, such as projectionsand recesses and the like of the sample, can be recognized.

However, as set forth above, methods employing electron beams presentproblems in that the inspection speed is slow requiring a longprocessing period.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems in theprior art and thus provide a pattern inspection apparatus that candetect defects in circuit patterns on inspection samples, such as masksor wafers or the like, by scanning at least one electron beam on theinspection sample and using secondary or backscattered electrons fromthe inspection sample or electrons transmitted through the sample withhigh sensitivity and high process speed, and thus has a large capacityfor information and a high processing speed for processing the patternof masks or wafers or the like having high density circuit patterns andhigh package density.

According to the present invention, there is provided a patterninspection apparatus which comprises:

an electron beam generator including an electron gun for generating atleast one electron beam which is accelerated and converged into apredetermined diameter and irradiated onto an inspection sample;

a movable support for supporting the inspection sample;

a detector unit including a plurality of electron detecting elementsarranged on a plane for detecting electrons containing constructioninformation relating to the inspection sample; and

a signal processor for processing information output from said electrondetecting elements simultaneously or in parallel.

With the construction set forth above, the present invention can detecta fine pattern on a mask, wafer or the like with high accuracy. Also,according to the present invention, the electrons transmitted throughthe sample or generated from the surface of the sample, and whichcontain information concerning the structure predetermined portions ofthe pattern, can be processed simultaneously or in parallel tocontribute to the shortening of the process period.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the detaileddescription set forth below and from the accompanying drawings of thepreferred embodiments of the invention, which, however, should not betaken to be limitative to the invention but are for explanation andunderstanding only.

In the drawings:

FIGS. 1(a) and 1(b) are schematic block diagrams showing practicalembodiments of a pattern inspection apparatus according to the presentinvention;

FIG. 2 is a fragmentary cross-sectional view of one embodiment of thepattern inspection apparatus of the invention;

FIGS. 3(a) to 3(c) are illustrations showing the principles of patterninspection when the pattern inspection apparatus of FIG. 2 is employed;

FIG. 4 is an illustration showing the principles of pattern inspectionwhen the pattern inspection device illustrated in FIG. 2 is employed;

FIG. 5 is a schematic illustration showing the construction of adetector 4 to be employed in the pattern inspection apparatus accordingto the invention;

FIG. 6 is a schematic illustration of another construction of a detector4 to be employed in the pattern inspection apparatus according to theinvention;

FIG. 7 is a diagram showing an example of a construction of a movablesupport 3 to be employed in the pattern inspection apparatus of theinvention;

FIG. 8 is a diagram showing an example of an electron beam generator 2to be employed in the pattern inspection apparatus of the invention;

FIGS. 9(a) and 9(b) are illustrations showing the irradiating electronbeam conditions when the electron beam generator 2 of FIG. 8 isemployed;

FIG. 10(a) is a side elevational view showing the overall constructionof another example of an electron beam generator 2 employed in thepattern inspection apparatus according to the invention, and FIG. 10(b)is a partial enlarged view of the generator of FIG. 10(a);

FIG. 11 is an illustration showing an example of an inspection processemploying a plurality of electron beams generated by the electron beamgenerator 2 of the invention;

FIG. 12 is an illustration showing an example of the construction of anelectron beam generator 2 and detector 4 used for detectingbackscattered or secondary electrons;

FIG. 13 is an illustration showing an example of a construction foroscillating or scanning the electron beam generator 2 in the patterninspection apparatus of the invention;

FIG. 14 is an explanatory illustration showing scanning characteristicsof electron beams using the apparatus of FIG. 13;

FIG. 15 is an illustration showing an example of a driver for theelectron beam generator 2 for performing simultaneous inspection ofadjacent samples in the pattern inspection apparatus according to theinvention;

FIG. 16 is an illustration showing an example of an inspection judgementcircuit for use when the driver of FIG. 15 is employed;

FIG. 17 is a plan view showing an example of a pattern inspectionperformed employing the driver of FIG. 15;

FIG. 18 is an illustration showing examples of defective portions to bedetected through pattern inspection;

FIG. 19 is a block diagram showing the principles of operation of apattern inspection apparatus according to the invention;

FIG. 20 is a block diagram showing a first embodiment of the patterninspection apparatus of the invention;

FIGS. 21(a) to 21(e) are diagrams which show waveforms in variousportions of the pattern inspection apparatus of FIG. 20;

FIG. 22 is a cross-sectional view showing the construction of anelectron beam irradiating generator portion of the embodiment of FIG.20;

FIG. 23 is a view which is similar to FIG. 22 but showing a secondembodiment of the pattern inspection apparatus according to theinvention;

FIG. 24 is another view which is similar to FIG. 22 but showing a thirdembodiment of the pattern inspection apparatus according to theinvention;

FIG. 25 shows the major components of a conventional pattern inspectionapparatus;

FIG. 26 is an illustration showing an example of a drawback due to thefluctuation of spot diameter in the prior art;

FIG. 27 is an illustration showing an example of a drawback due to thefluctuation of deflection angle in the prior art;

FIG. 28 is a diagram showing the principles of another embodiment of thepattern inspection apparatus according to the invention;

FIG. 29 is a diagram showing the major components of another embodimentof the pattern inspection apparatus of FIG. 28;

FIGS. 30(a) and 30(b) are schematic views showing the details of themajor components of a circuit C_(i) with a plan view including thecircuit C_(i) ;

FIG. 31 is an illustration of a connection when an electrode voltageVdzi of a converging electrode Edzi is adjusted;

FIGS. 32(a) and 32(b) are illustrations showing a layout of the basicpattern in an embodiment of the invention;

FIGS. 33(a) to 33(c) are conceptual illustrations showing a way tomeasure a spot diameter in a knife edge method according to anembodiment of the invention;

FIGS. 34(a) and 34(b) are conceptual illustrations showing another wayto measure spot diameter using a light metal and a heavy metal accordingto another embodiment of the invention;

FIGS. 35(a) to 35(c) are illustrations showing an embodiment of thepattern inspection apparatus according to the invention;

FIG. 36 is an illustration showing an embodiment of the patterninspection apparatus according to the invention;

FIG. 37 is an illustration showing an arrangement of an embodiment of adetection element of the invention;

FIG. 38 is an illustration showing an example of the arrangement of adetection device according to an embodiment of the invention;

FIG. 39 is an illustration showing an embodiment of the patterninspection apparatus according to the invention;

FIGS. 40(a) and 40(b) are illustrations showing the construction of asignal processing section in an embodiment of the pattern inspectionapparatus of the invention;

FIG. 41 is an illustration showing detection signals upon the presenceand absence of a pattern;

FIGS. 42(a) to 42(c) are illustrations showing an embodiment of thepattern inspection apparatus in which FIG. 42(a) is a fragmentaryillustration showing a concept of the embodiment, FIG. 42(b) is a planview of a mask formed with openings and FIG. 42(c) is a graph foridentifying a portion of the mask having an opening.

FIGS. 43(a)-1 to 43(d) are illustrations showing wave forms used in amodulation method in another embodiment of the present invention;

FIG. 44 is an illustration showing a switching circuit used in thepresent invention;

FIG. 45 is an illustration showing another type of switching circuitused in the present invention; and

FIG. 46 is an illustration showing a real time controlling circuit usedin the present invention.

FIGS. 47(a) and 47(b) show a principle of another embodiment of presentinvention;

FIGS. 48(a) and 48(b) show an electrostatic eight-pole electrode;

FIG. 49 is an explanatory illustration of the electrostatic eight-poleelectrode;

FIG. 50 is an illustration explaining the production of theelectrostatic eight-pole electrode;

FIGS. 51(a) and 51(b) are illustrations explaining how to produce theelectrostatic eight-pole electrode;

FIGS. 52(a) and 52(b) are illustrations explaining another method ofproducing the electrostatic eight-pole electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of a pattern inspection apparatus according tothe present invention will be discussed herebelow in detail withreference to the accompanying drawings.

FIG. 1(a) provides a brief illustration of one embodiment of the patterninspection apparatus according to the present invention. FIG. 1(b)provides a brief illustration of another embodiment of the patterninspection apparatus according to the invention.

In both of the embodiments of FIGS. 1(a) and 1(b), a pattern inspectiondevice 1 comprises an electron beam generator 2 having an electron gunfor generating at least one electron beam that is accelerated andconverged into a predetermined diameter for irradiating an inspectionsample, a movable support 3 for supporting the inspection sample, adetector 4, which includes a plurality of electron detecting elementsfor detecting the electron containing information associated with theconstruction of the inspection sample arranged in alignment, and adetection signal processor 5 for processing information output fromrespective electron detecting elements of the detector 4 simultaneouslyor in parallel formation.

FIG. 1(a) is basically designed for an inspection of a circuit patternby transmitting an electron beam through the inspection sample, such asa mask or the like. On the other hand, the apparatus of FIG. 1(b) isbasically adapted to use secondary or backscattered electrons generatedin the inspection sample by irradiating the electron beam onto aninspection sample, such as a wafer, for performing an inspection.

A discussion of the electron beam generator 2 to be employed in thepreferred embodiment of the pattern inspection apparatus according tothe present invention follows. As set forth above, conventional methodsemploying a light beam have limited resolution due to diffractioneffects, and therefore, such methods are not suitable for patterninspection of masks or wafers or the like having high circuit patterndensity and high package density. In contrast to this, according to thepresent invention, an electron beam of charged particles is basicallyemployed. In addition, in the illustrated embodiments of the patterninspection apparatus according to the present invention, the electronbeam generator 2 is designed to generate a highly converged electronbeam.

An example of the electron beam generator 2 comprises an electron gun21, and an electron optical system 25 including an electromagnetic lens22, a deflector 23 and an electromagnetic lens 24.

In the drawings, the movable support 3 comprises a sample stage 31 forsupporting an inspection sample S, such as a mask or the like, an XYstage drive mechanism 32 for shifting the sample stage 31 horizontallyin one dimensional or two dimensional directions, and a laserinterferometer 33, for example, for detecting the position of the samplestage 31 and generating a control information signal.

As shown in FIG. 2, a detector 4 composed of a plurality of electrondetecting elements is provided beneath the movable support 3. Thedetector 4 is designed to receive a plurality of electron beams and toprocess the same simultaneously or in parallel formation. The output ofthe detector 4 is processed by a detection signal processor 5 thatcomprises an amplifier 51 and a signal processing circuit 52.

In a conventional method for fabricating a circuit pattern T on a waferor the like, a single electron beam is employed so that the electronbeam, which is finely focused by means of an appropriate electromagneticoptical system, is irradiated onto the wafer and scanned along theintended pattern T so as to form an image of the pattern T.

In contrast the present invention employs an electron beam forperforming an inspection to check whether a circuit pattern has beencorrectly drawn. Therefore, in the electron optic system 25 of FIG. 2,the electron beam from the electron gun 21 is converged by a converginglens 22, such as an electromagnetic lens or the like, into apredetermined beam size, and then the converged beam may then beirradiated onto random positions in a certain region of the mask bymeans of the deflector 23. Therefore, an appropriately convergedelectron beam is irradiated onto a given region of the circuit patternas shown in FIG. 3a. According to the present invention, the beamdiameter of the electron beam is adjusted by the electron optic system25 so that the given region of an inspection sample can be irradiateduniformly.

As shown in FIG. 3b, in the X-ray mask or the like, the substrate 26 isa thin film made of a material containing elements having a relativelysmall atomic weight, such as SiC. On such substrate 26, an absorber 27made of a material containing an element having a relatively largeatomic weight, such as gold or tantalum is patterned for absorbingX-rays. When the electron beam is irradiated onto such mask S, theportion of the electron beam B irradiated on the absorber 27 isscattered by the heavy elements thereof so that the electrons of thebeam do not pass through the mask and the same are not significantlyscattered. On the other hand, the substrate 26 is in the form of a thinfilm having a thickness of about 2 μm, and very little scattering of theirradiated electron beam occurs. Therefore, the width of the scatteredelectron beam remains sufficiently small so that most of the electronspass through the substrate 26.

Accordingly, as shown in FIGS. 3(c) and 4, only those electrons whichare transmitted through the substrate 26 form the expanded image on thedetector 4 using an appropriate electron optic system 6. Sincetransmitted electrons are detected, dust, which does not significantlyeffect X-rays and is detected as a defect when conventional methods fordetecting secondary or backscattered electrons are used, permits theelectron beam to pass without absorbing a significant part thereof so asnot to produce a detection error signal in the prior art.

As set forth above, according to the present invention, the electronbeam B generated in the electron beam generator 2 and thereafter shapedis irradiated onto the inspection sample S, such as a mask or the like.Then, the transmitted electrons containing two dimensional informationof the inspection sample are projected onto the detector 4 through theelectron optic system 6 to form the pattern image T on the detector 4.

On the other hand, in the detector employed in the embodiment of thepattern inspection apparatus as shown in FIG. 5, a plurality of electrondetecting elements 41, such as semiconductor detecting elements formedby PN junction elements, are arranged in horizontal alignment in one ortwo dimensional directions. Each of the electron detecting elementsreceives an electron beam transmitted through an inspection sample S andgenerates an electric signal corresponding to the intensity of theelectron beam.

On the other hand, as the detector 4, a channel plane 41, such as thatillustrated in FIG. 6, can also be employed.

In this case, the electrons entering the channel are boosted to enhanceS/N ratio. As set forth above, the mask pattern thus formed can beobtained as a two dimensional image.

The detection signals are generated by the detector 4 are processed,such as by binarization, simultaneously or in parallel formation, by thesignal processing portion 5 and transmitted to a memory section or thelike and stored therein as digital image signal. Subsequent processingfollowing the image processing is similar to that performed in aconventional mask inspection apparatus. Namely, such processing is doneby comparing the image information of the same pattern of two chips todetect a difference therebetween to determine the presence of a defect.As an alternative, the defect can be detected by comparing obtained datawith design data.

It should be noted, that in the movable support 3 of the presentinvention, as shown in FIG. 7 for example, the inspecting sample S, suchas a mask or the like, is fixed to the sample stage 31. The sample stage31 is rigidly fixed to an XY stage 32. For sample stage 31 and the XYstage 32, openings P are formed for allowing electrons to passtherethrough. The XY stage 32 is designed to be driven by means of anexternal driving motor 34 through a ball screw or the like.

The foregoing discussion has been provided for the case in which theinspection sample to be subjected to pattern inspection is a mask or thelike, which permits the electron beam to pass therethrough. However, thepresent invention can be equally implemented for the case in which theinspection sample S is a wafer or reticule having a substrate with athickness of several mm and thus does not permit the electron beam to betransmitted therethrough by using secondary electrons.

In such a case, as shown in FIG. 1b, the detector 4 is disposed betweenthe movable support 3 supporting the inspection sample S and theelectron beam generator 2. Other constructions should be understood asequivalent to those of the embodiment of FIG. 1a.

In such a case, the electron detecting elements 41 of the detector 4 areof course directed toward the movable support 3.

Furthermore, in the above-mentioned two examples of the presentinvention, the electron beam B generated by the electron beam generator2 may be scanned on the inspecting sample S appropriately by means ofthe deflector. Such construction may be combined with the movablesupport 3 so that the predetermined pattern T can be rapidly detectedwith high sensitivity for small defects and high accuracy.

In order to satisfy the requirement for processing a large amount ofdata for efficiently inspecting the inspection samples S, such as a maskor a wafer or the like, having high circuit density and high packagedensity, it becomes necessary to use a plurality of electron beamgenerating units. An embodiment employing a plurality of electron beamgenerating unit 25 is illustrated in FIG. 8. As can be seen,multi-construction of the electron beam generator 2 employed in theembodiment in FIG. 8 has a construction such that the electron beamgenerator 2 per se is divided into a plurality of sub-devices 25; eachsub-device 25 including at least an electron emitter 101, a convergingelectrode 102, and a deflection electrode 103 formed in a laminatedconstruction.

The electron beam generator 2 in FIG. 8 has a silicon substrate 100. Inthe silicon substrate, an electron emitter section 101 of silicon orhexagonal boron lanthanum is formed. On the same or separate siliconsubstrates, a plurality of silicon oxide (SiO₂) layers and apolycrystalline silicon layer are appropriately formed and theconverging electrode 102 and the deflection electrode 103 are formedtogether with holes for passing electrons using fine processingtechnology. Then, the sub-assemblies thus formed are combined to obtaina multi-construction electron beam generator 2 which includes aplurality of individual electron beam generating units 25.

The electron beams generated by the respective units 25 of the electronbeam generator means 2 of the FIG. 8 embodiment have identical diametersand the same are adapted to uniformly irradiate predetermined areas of aplurality of regions on the inspection sample S.

In order to implement the pattern inspection apparatus according to theinvention in a practical sense, it is, of course, possible to use theelectron beam generator 2 of FIG. 2, which generates a single electronbeam. However, in view of efficiency of inspection, it is preferred toemploy an electron beam generator 2 as illustrated in FIG. 8 whichincludes a plurality of beam generating units 25.

When a beam generator 2 having a plurality of the electron beamgenerating units is employed, such electron beam generating units can bearranged in a single dimensional direction or in two dimensionaldirections.

It should be appreciated that the number of rows or columns and thearrangement pattern of the plurality of electron beam generating unitsare not specified and can be determined in any number and any patterndepending upon intended application.

Particularly, as shown in FIG. 9a, on the circuit pattern T formed onthe inspection sample S, a plurality of electron beams B1, B2, B3, B4 .. . Bn are irradiated simultaneously so that respective electrondetecting elements 41 of the detector 4 may detect the transmittedelectrons or backscattered secondary electrons. Therefore, by employingthe multi-construction electron beam generator 2, a fine and largeamount of pattern information can be quickly and accurately obtained forenhancing efficiency of inspection.

On the other hand, when a plurality of the electron beam generatingunits 25 are employed, each individual electron beam generating unit 25may be designed to scan its respective electron beam B1, B2, . . . overa predetermined region by the deflection electrode 103.

By employing such a construction to permit scanning of the electronbeam, it becomes possible to enable quick inspection for anyconfiguration of circuit pattern on the inspection sample S by usingscanning of the electron beam in combination with horizontal shifting ofthe movable support 3.

In order to positively form a plurality of electron beams B, anotherconstruction of the electron beam generating means 2 as illustrated inFIGS. 10(a) and 10(b) can be employed.

In the embodiment of FIGS. 10(a) and 10(b), a fine constructionsubstrate 110 includes a converging electrode 102 and a deflectionelectrode 103. The electron emitter 101 for use as an electron gun isomitted. As shown in FIG. 10(a), the fine construction substrate 110 isdisposed between an electron beam generator 2 composed of an electrongun 21 and an optical system 22 and the movable support. Then, anelectron beam injected from the electron gun 21 and having an uniformdiameter formed by the optical system 22 is caused to pass through apredetermined number of electron beam passing holes 111 havingpredetermined configurations so that a plurality of electron beams areirradiated simultaneously on the surface of the inspection sample S.

In addition, by respectively controlling the deflection of theindividual electron beams passing through the electron beam passingholes 111 by the converging electrode 102 and the deflection electrode103, a plurality of regions on the inspection sample can be scannedsimultaneously.

In the method set forth above, part of the circuit pattern on theinspection sample S can be inspected at one time. By using the deflectorfor scanning the electron beam in combination with the operation of themovable support 3, the area to be inspected during a single inspectingoperation can be expanded.

Therefore, in accordance with the present invention, after inspection ofone part of the region of the pattern T on the inspection sample S iscompleted, the movable support 3 is shifted by means of the XY stage 32to shift the irradiating region of the electron beam.

As shown in FIG. 11, the detectors 4 have a size corresponding to asmall region. In each region, the electron detecting elements 41 of thedetector 4 detect the presence and absence of the transmitted electronsin synchronism with the scanning of the electron beam to obtain patterninformation from respective positions on the mask.

FIG. 12 shows the pattern inspection apparatus according to the presentinvention, which is designed for detecting secondary electrons orbackscattered electrons from a mask or wafer on which the electron beamis irradiated. In the shown construction, the detector 4 has a pluralityof electron detecting elements 41 formed in the substrate 100, on whichthe electron beam generator 2 is provided.

In the method of pattern inspection according to the present invention,each of the electron detecting elements 41 is coupled with acorresponding electron beam so as to detect the secondary electrons orthe backscattered electrons from the irradiating position of thecorresponding electron beam. Since the electron beams and the electrondetecting elements 41 are driven integrally, the secondary electrons orthe backscattered electrons from an adjacent beam will be detected asmere noise. Therefore, degradation of a S/N ratio due to scattering ofan adjacent electron beam does not occur. The detection signal from eachdetecting element 4 is transmitted to the signal processing section andsubjected to parallel image processing, such as binarization. Theresultant digital image signal is stored in the memory section. Theimage processing to be subsequently performed is similar to thatperformed in a conventional inspection apparatus.

In accordance with the present invention, it is possible to oscillatethe electron beam generator 2 per se within a predetermined region or toshift the electron beam generator 2 in two dimensional directions usinga driving section 35, instead of employing a deflector 103 in theelectronic beam generator described above, and as shown in FIG. 13. Withsuch a construction, as shown in FIG. 14, the electron beams B1, B2 canbe irradiated in predetermined regions of the inspection sampleuniformly in a relatively wide range. Therefore, the electron beam B isdriven so as to shift at high speed within a predetermined appropriatepattern by the driving section 35. This makes a qp [provision of thedeflecting optical system 103 unnecessary for the electron beamgenerator 2.

The electron beam generator 2 is mounted on an oscillation stage that iscaused to oscillate in a very small range at high speed by the drivingsection 35. When a piezoelectric oscillation actuator, such as apiezoelectric element or the like, is employed for driving theoscillation stage, high speed oscillation at a frequency of several 10Khz in a range of several 100 um can be realized.

In a practical construction of the pattern inspection apparatusaccording to the present invention, two of the above-mentioned patterninspection mechanisms are provided for simultaneously inspecting twoseparate chips. The two pattern inspection mechanisms are at identicalpositions so that the same locations of the chips can be inspected. Thepositions of the pattern inspection mechanisms are variable dependingupon the size of the chips to be inspected. The positions of the patterninspection mechanisms are variable depending upon the size of the chipsto be inspected. As illustrated in FIG. 15, the electron generators 2-1and 2--2 are mounted on fine adjustment stages 28 and 29 respectively,which can be moved by a slide 27 for adjusting the distance betweenstages. It is possible to apply a piezoelectric oscillation element oneach sample supporting stage. Furthermore, it may also be possible tocause shifting of the electron beam in the X direction by theabove-mentioned mechanical scanning means and to scan the electron beamin the Y direction using an electrostatic deflection electrode 103 (orvice versa).

In the present invention, as shown in FIG. 16, the inspection samples S1and S2 are mounted on the movable support 3. Samples S1 and S2 areirradiated by electron beams in unison so that respective correspondingelectron detecting elements 41₁ and 41₂ detect the secondary orbackscattered electrons reflected from the irradiated position to outputthe detection information. The detection information is processed by theamplifier 51 and the image memory 53 and the processed information isthen compared in the detecting signal processing circuit 52.

FIG. 17 is a plan view illustrating a practical method for performing acomparison of the detected patterns of the samples S1 and S2. When thechip pattern TI of the inspection sample S1 and the chip pattern T2 ofthe inspection sample S2 are compared, the first electron beam generator2-1 and the second electron beam generating means 2--2, between whichfine adjustment of distance is effected, are scanned according to apredetermined scanning pattern by the driving section 35. In addition,if required, by providing fine oscillation, a predetermined deflectionis provided for the electron beam B. As an alternative, by employing thedeflector incorporated in the electron beam generator, a predetermineddeflection is provided for the electron beam B. In this way, the patternT in the predetermined region can be completely scanned and inspected.

With the practical embodiments set forth above, by irradiating at leastone electron beam to a predetermined region on the inspection sample,such as a mask or wafer or the like, and by using secondary electrons orbackscattered electrons reflected from the sample or electronstransmitted through the sample, the defects in the circuit pattern onthe inspection sample can be detected with satisfactorily highsensitivity and resolution and at high speed. Accordingly, it becomespossible to provide a pattern inspection device that can be adapted toan increase of the fineness of the circuit pattern and to an increase inthe package density.

In addition, when an inspection is performed on an inspection sample,such as an X-ray mask or the like, by detecting transmission electrons,detection errors caused by dust can be successfully prevented to enhancethe accuracy of the inspection.

Next, another embodiment of a pattern inspection apparatus according tothe present invention will be discussed.

With the foregoing embodiment, the objects of the present invention canbe attained. However, in the case of the pattern inspection apparatusthat employs a plurality of parallel scanning electron beams, therespective electron flow entering the corresponding electron flowdetecting sections may be interfered with by electrons from an adjacentirradiation region. This degrades the S/N ratio at the boundary regionsbetween adjacent irradiated regions.

Therefore, by solving the above-mentioned problem, the effect of thepresent invention can be improved. Thus, the embodiment described abovemay be adapted for achieving a shortened inspection time as well as forproviding an enhanced S/N ratio at the respective electron irradiationregions.

As set forth above, when a single electron beam is irradiated onto thepredetermined region of the inspection sample for detectingbackscattered electrons or secondary electrons generated by suchirradiation by the corresponding detecting section, the secondaryelectrons generated in an adjacent inspection region can be superimposedon the backscattered or secondary electrons from the region beinginspected. In such a case, an error, such as when the presence of apattern is detected even though a pattern is not present in theinspection region, can result.

For avoiding superimposition of the secondary electrons from theadjacent inspection region, various proposals have been made. In theshown embodiment, a plurality of electron beams are modulated into apulse so that the pulse period of respective electron beams irradiatingrespective adjacent inspection regions are differentiated from eachother. Upon detection of secondary electrons from a respectiveinspection region, the pulse period of the electron beam is synchronizedso that only the synchronized pulse is processed for inspection. As analternative, the pulse width of the electron beams may be set atspecific known values, and measurement of the secondary electrons of thecorresponding inspection region may be controlled so as to take placeonly in response to the occurrence of the specific pulse width of theelectron beam.

In addition, in the shown embodiment, the electron beams consisting ofpulses having different periodicities are subject to a time-divisionbased multiplexing process so that the secondary electrons of the regionto be inspected is measured in synchronism with the specific pulse.

Also, in the shown embodiment, a plurality of electron beams arerespectively modulated and composed so as to form a modulated electronbeam. With this modulated electron beam, the secondary electron beam ofthe region to be inspected is measured in synchronism with the specificpulse width.

In the shown embodiment, the electron beam may also be processed to forma pulse or to be modulated so that a time difference is provided in themeasurement timing of the secondary electrons at respective inspectionregions to avoid any influence from secondary electrons from adjacentinspection regions.

In the present invention, the modulating process includes a time-sharingprocess and a detection method as well as an ordinary modulationprocess.

FIG. 19 shows the use of such principles in connection with anembodiment of the pattern inspection apparatus according to the presentinvention. The apparatus of FIG. 19 includes an electron beam supplysource 301, an electron beam modulating unit 302 an electron beamscanning unit 303, an electron flow detecting unit 304, a signalprocessing section 305 which processes an incoming modulation signal 1.The apparatus is used to inspect the inspection sample 310. It should benoted that the shown embodiment is directed to an example employing twoelectron beams. Also, the electron beam scanning unit 303 is shown as amechanical scanner for shifting the electron beam supply source 301.

In order to accomplish above-mentioned objects, the pattern inspectionapparatus according to the present invention comprises an electron beamsupply source 301 for supplying electron beams respectively irradiatedonto a plurality of irradiating regions of an inspection sample, anelectron beam modulating unit unit 302 for modulating the respectiveelectron beams into modulated signals having mutually distinct signalpatterns, an electron beam scanning unit 303 for shifting theirradiating position of respective electron beams in order, an electronflow detecting 304 for detecting the electron flow from the inspectionsample 310 generated by the electron beam and including informationrelating to the construction of a respective irradiated region, and asignal processing section 305 for extracting a signal representative ofthe construction of a respective irradiating region from the outputsignal of the electron flow detecting unit 304.

Respective electron beams supplied through the electron supply source301 are modulated into the mutually distinct patterns of modulatedsignals by the electron beam modulating unit 302. The modulated signalsof the electron beams are scanned on respective irradiating regions onthe inspection sample via the electron beam scanning unit 303. Theelectron flow generated at respective irradiated regions by irradiationof the electron beams are gathered by incidence to the common electroncurrent detecting unit 304 and subsequently input to the signalprocessing section 305. The signal processing section 305 thus derivessignals indicative of the construction of respective irradiated regions.

Further detailed discussion about the foregoing embodiment will be givenhereafter with reference to the drawings. FIG. 20 shows, in the form ofa diagram, the construction of the shown embodiment of the patterninspection apparatus. In FIG. 20, an electron generating element 411forming a part of the electron beam supply source includes a pluralityof electron emitters 411 and 412 on a common plane. The electronemitters 411 and 412 emit electron beams 361 and 362. The electron beams361 and 362 are modulated by modulating electrodes 321 and 322 that formthe electron beam modulating unit and which receive a modulating signalfrom the signal processing section 305.

The electron beams 361 and 362 pass a common converging electrode 312that converges respective electron beams in a respective fine area, anddeflection electrodes 331 and 332 are provided for respective electronbeams 361 and 362 to reach the inspecting sample 310. The convergingelectrode 312 forms a part of the electron beam supply source. Thedeflection electrodes 331 and 332 scan respective irradiation regions401 and 402 of the inspection sample by shifting the electron beams 361and 362 in order within the irradiating regions 401 and 402.

The inspection sample 310 is fixed on the sample stage 309. The samplestage 309 is adapted to be shifted in X, Y and Z directions viarespective XYZ stage shifters. The XYZ stage shifters are designed to bedriven by respective drive motors through ball screws or the like. Whenscanning the electron beam on respective irradiation regions 401 and402, the deflection electrodes 331 and 332 are used, and the XY stageshifter motors are driven for scanning another irradiation region of theinspection sample 310.

On the upper portion of the inspection sample 310, the common electronflow detecting section 304 is provided to commonly detect thebackscattered electrons 371 and 372 generated by irradiation of theelectron beams 361 and 362 on respective irradiation regions 401 and402. The output of the electron current detecting section 304 is inputto the signal processing section 305.

The signal processing section 305 comprises a CPU 351 for controllingthe overall pattern inspection apparatus, modulated signal generatingsections 352 and 353 for providing the modulating signals for respectivemodulating electrodes 321 and 322 via amplifiers 357 and 358, a signaldiscrimination section 354 for discriminating the configuration signalsfrom the irradiation regions 401 and 402 taking respective modulatedsignals from the modulating signal generating sections 352 and 353 asreference signals, an image processing section 355 for receiving theoutput of the signal discriminating section 354 to convert theinformation contained therein into a binary image signal, and a memorysection 356 for storing the binary image signal.

FIGS. 21(a) through 21(e) FIGS. 21(a) through 21(e) show waveforms ofthe signals to be used for discussion about respective signals in apattern inspection apparatus. In this embodiment, the modulating unitforms pulses of the sequence of the electron beam for alternativelyusing two pulses having mutually different pulse phases. In the presentinvention, the modulation method includes a method for making a pulsesignal from a continuous beam. The modulated pulse signals illustratedin FIGS. 21(a) and 21(b) are pulse signals having mutually similar pulsefrequencies and peaks thereof appear in alternative fashion. Namely, theshown embodiment is directed to the example of signal processing intime-division multiplexing.

The signals of the electron flow gathered in the electron detectingsection 304 by incidence thereon from respective irradiation regions isillustrated in FIG. 21(c) as the input for the signal discriminatingsection. Namely, when the modulated pulse signal 1 is at the level H,the input signal for the signal discriminating section discriminates thesignal as the configuration signal of the irradiation region 401. On theother hand, when the modulated pulse signal 2 is at the level H, thesignal discriminating section discriminates the input as theconfiguration signal of the irradiation region 402.

In the signal discriminating section 354, by employing the pulse signal1 as the reference signal, an output as illustrated in FIG. 21(d) may beobtained as the configuration signal of the irradiation region 401. Onthe other hand, by employing the pulse signal 2 as the reference signalfor discrimination, the output 2 illustrated in FIG. 21(e) is obtainedas the configuration signal of the irradiation region 402. The amplitudeof these outputs represents the pattern at respective irradiationregions 401 and 402. These signals are thus discriminated by the signaldiscriminating section 354 and converted into digital signals by theimage processing section 355 in parallel with one another.

The output of the image processing section 355 is stored in the memorysection 356 as digital image information. By a signal processingsection, which is not shown and follows the memory section 356,conventional signal processing is performed for implementing a patterninspection.

An example is given to the signal frequency to be used. When the periodduring which each electron beam is processed and modulated into a pulsesignal, and namely, the period during which an electron remains on thepulse generating electrode, is 500 nsec, approximately 2 Mhz is used asthe frequency of the pulse signal. In such a case, assuming the totalnumber of irradiation regions to be irradiated in parallel formationaccording to the present invention is 100, and by employing time-sharingmultiplexing, the pulse width of a respective modulated pulse signalbecomes 500 nsec./100=5 nsec. Accordingly, in such time sharingmultiplexing of pattern information of the inspection samples, itbecomes possible to perform an inspection for 2M×100 each second.Namely, 200 pixel/seconds is possible.

On the other hand, instead of using timesharing multiplexing, it ispossible to use pulse signals having the same frequency and mutuallydifferent pulse widths, and even in this case, the signal discriminationtaking the moduled signals as reference signals is similar to the formerembodiment.

FIG. 22 shows a cross-section of the construction details of theelectron beam irradiating portion in the embodiment of FIG. 20. As shownin FIG. 22, electron beams are supplied by an electron beam generatingsection 311, the converging electrodes 421 to 423 form a three stagelens, and modulating electrodes 321 and 322 are disposed therebetween.Deflection electrodes 331 and 332 are provided between the convergingelectrodes and the sample 310.

In the construction of the electron beam irradiating portion, theelectron beam generating section 311, the modulating electrodes 321 and322, the converging electrodes 421 to 423 and the deflection electrodes331 and 332 are preferably formed on a silicon substrate employing fineprocessing technology. Such construction has been reported in G. W.Jones et al. "Microstructure for Particle beam Control", J. Vac. Sci.Technol. pages 2023 to 2027, B6(6), November/December 1988, for example.

As shown in FIG. 22, the converging electrode is formed of threeelectrostatic lens stages 421, 422 and 423 arranged along the travelingdirection of the electron beams 361 and 362. The front stageelectrostatic lens 421 is set at a high potential with respect to theelectron beam generating section 311 and such lens is commonly used asan output line for extracting electrons from the electron emitters 411and 412.

The rear stage electrostatic lens 423 is maintained at an equalpotential to the front stage electrode 421. The intermediate electrode422 is maintained at a different potential than the electrodes 421 and423. The three stage electrostatic converging lens converges theelectron becomes emitted from the electron emitters 411 and 412otherwise have a tendency to be scattered.

The modulating electrodes 321 and 322 modulate electron beams 361 and362 into pulses according to the modulating signals. In such a case, thepeaks of the modulating signal become equal in potential to the electronbeam generating section 311 so as to permit generation of the electronbeam, and the valleys of the pulse of the modulating signal reach anegative value so as to shut the front stage electrostatic lens 421 andblock the emission of electrons to thus control the amount of electronsgenerated from the electron beam generating section 311.

The deflection electrodes 331 and 332 are provided the same scanningsignals so that scanning voltages are applied between the deflectionelectrodes respectively in opposing X and Y directions. By deflectingthe electron beams simultaneously in the same direction according to thescanning voltage, scanning of respective irradiating regions occurssimultaneously.

The manner of scanning is illustrated in FIG. 14. The electron beams 361and 362 converging at the irradiation regions 401 and 402 by the effectof the converging electrodes are shifted in four directions parallel tothe irradiation surfaces of respective irradiation regions 401 and 402of the inspection sample by respectively corresponding deflectionelectrodes, as illustrated by arrows, so that all areas in theirradiation regions 401 and 402 can be scanned.

FIG. 23 is a cross-sectional view showing another construction of theelectron beam irradiating portion in the pattern inspection apparatusaccording to the present invention that corresponds to that illustratedin FIG. 10. In FIG. 23, the electron beam generating section isdifferentiated from that shown in FIG. 22 and comprises an electronsupply source 317 for supplying electrons uniformly, and a shieldingplate 318 having fine apertures 481 and 482 at positions correspondingto respective irradiation regions for allowing electron beams to passtherethrough. An accelerating voltage is applied at a position betweenthe shielding plate 318 and the front stage electrostatic lens 421 foraccelerating the electrons. Otherwise, the construction is the same asthat of FIG. 22.

FIG. 24 is a cross-sectional view showing the electron beam irradiatingportion of a third embodiment of the pattern inspection apparatusaccording to the present invention. In this embodiment, in place of themodulating electrodes 321 and 322 for modulating the electron beam asillustrated in FIG. 22, the apparatus includes deflection modulatingelectrodes 323 and 324 for deflecting the electron beams 361 and 362 ina direction perpendicular to the traveling direction as illustrated bybroken line A, and passing control sections 325 and 326 having walls 451and 461 for blocking the deflected electron beam by. Otherwise theconstruction is the same as that of FIG. 22. The signal waveform in thisembodiment is similar to that shown in FIG. 21 and therefore discussionthereof is omitted.

In the embodiment of FIG. 24, by sequentially deflecting the axis of theelectron beam transversely, a pulse form electron beam is irradiatedonto the irradiation region.

FIG. 43 shows signal wave forms used in another embodiment of themodulating method of the present invention in which each of the mainpulse wave signals is modulated by adding thereto a plurality ofadditional pulsed signals, each having a different frequency and themain pulse wave signal per se can be discriminated from the detectedsignal, the plurality of additional pulsed wave signals being integratedinto the main pulse wave signal by tuning the main pulse wave signal atthe same frequency as the main pulse wave signal originally had.

For example, FIG. 43 (a)-1 shows the wave form of the main pulse wavesignal in a beam used in the present invention while FIG. 43 (a)-2 showsthe wave form of the noise caused by an interference signal generated byadjacent pulse wave signal beams.

The main pulse wave signal has a frequency different from that of theinterference signal and FIG. 43(a)-3 shows the wave form of a modulatedpulsed wave signal in which the main pulse wave signal 1 is modulated bythe noise pulse wave signal 2 and thus a detector detects the pulse waveform 3 which has the noise incorporated therein.

Note, that in FIG. 43(a)-3, a dotted line represents the true pulse waveform of the main pulse wave signal 1.

FIG. 43(b) shows the pulse wave form of a modulated pulsed wave signalin which the main pulse wave signal 1 is interfered with by a pluralityof pulsed noise wave signals, each having a different frequency.

In this embodiment, the pulse wave signal shown in FIG. 43(b) is formedby modulating the main pulse wave signal 1 with a plurality of pulsednoise wave signals.

FIG. 43(c) shows a modulated wave form obtained from the pulse wave formof FIG. 43(b) by passing it through a band-pass filter having the samefrequency as the original frequency of the main pulse wave signal as acenter of the band. Continuous line 5 represents the wave form of themodulated wave form of the pulse wave signal 1 in which both the highfrequency components and the low frequency components are deleted fromthe final wave form.

The wave form as shown in FIG. 43(c), for example, represents a signallevel which indicates that the pulse wave signal 1 is used to detectwhite patterns, i.e., the fact that patterns exist.

On the other hand, FIG. 43(d) shows a modulated wave form obtained fromanother pulse wave form generated in a condition in which no patternexists in the same way as explained above, and the continuous line 6represents a signal level showing that the pulse wave signal is used todetect black patterns, i.e., the fact that no pattern exists.

Accordingly, whether or not a pattern exists on the substrate, can bediscriminazed by detecting the difference of amplitudes of the twoseparate wave forms.

With the shown construction, a plurality of irradiation regions can bescanned by electron beams simultaneously enabling high speed inspection.Also, interference between adjacent electron beams can be successfullyprevented so as to obtain configuration signals with an enhanced S/Nratio. Therefore, the shown embodiment of the pattern inspectionapparatus can perform accurate inspections in a short inspection period.

Although the foregoing embodiment attains a remarkable improvement ofthe efficiency of inspection and avoids mutual interference of adjacentelectron beams, the following unsolved problem remains.

Namely, the foregoing pattern inspection apparatus according to thepresent invention, is composed of a plurality of electron guns, beamextracting electrodes, converging electrodes and deflection electrodes.When respective electron guns or respective electrodes includeproduction tolerances, slight variations are induced in thecharacteristics of the electron beams so as to cause fluctuations of thefocus points of the electron beams. In some cases, the focus point isset in front of or behind the irradiation surface to cause focus errorat the image to be inspected. This problem is encountered not onlyduring pattern inspection but also in the drawing of patterns employingan electron beam exposure device. To solve this problem, the electronbeams emitted from a plurality of electron guns must be uniformlyirradiated onto the inspection surface. The following embodiment of thepattern inspection apparatus proposes a solution for this problem bycomparing each electrode with a preliminarily provided referenceelectrode so as to individually adjust the characteristics thereof andmake it consistent with that of the reference electrode.

The following is a discussion for this embodiment of the patterninspection apparatus according to the present invention.

FIG. 25 shows the construction of a major portion of an embodiment ofthe pattern inspection apparatus according to the invention. As shown inFIG. 25, the apparatus includes an electron beam generator 501. Theelectron beam generator 501 includes a silicon substrate 502, on which aplurality of (two are shown in the drawing) electron emitters 503 and504 are formed of silicon, a metal such as Ta or the like, or a compoundsuch as lanthanum boride or the like. Below the electron emitters 503and 504, a plurality of laminated layers are formed so as to prevent anextraction electrode 505, a converging electrode 506, a deflectionelectrode 507 and detectors 508 and 509 as shown. In FIG. 25, thereference numeral 510 denotes an anode, the reference numerals 511 and512 denote grounding electrodes, and the reference numeral 513 denotesan inspection sample, such as an exposure mask or the like, on which afine pattern (omitted from illustration) is formed.

The charged particle beams (electron beams) 503a and 504a emitted fromemitters 503 and 504 have a beam current corresponding to the electrodevoltage V₅ of the extraction electrode 505. The electron beams 503a and504a are then converged with a convergence ratio corresponding to theelectrode voltage V₆ of the converging electrode 506. Subsequently, theelectron beams 503a and 504a are deflected at a deflection anglecorresponding to the electrode voltage V₇ of the deflection electrode507 and are thus irradiated onto the sample 513 in the form of a spot.

Then, backscattered or secondary electrons (illustrated by broken lines)are discharged from the surface of the sample 513, for example an X-raymask in response to irradiation of the sample by the electron beams 503aand 504a. These emitted electrons are caught by the detectors 508 and509 and converted into electric signals, and a greater amount of emittedelectrons are emitted from the electron beam absorber than from the masksubstrate forming the sample 513, because the material (gold, tantalumand other elements having a large atomic weight) used for the electronbeam absorber has a higher generation ratio of backscattered electronsor secondary electrons than the material (silicon or other elementshaving a small atomic weight) used for the mask substrate.

Accordingly, by simultaneously irradiating a plurality of electron beams503a and 504a and unitarily processing the outputs of the detectors 508and 509 for the respective electron beams, a large amount of patterndata relating closely to the pattern formed on the surface of the sample513 can be inspected rapidly and accurately. Also, when the apparatus isapplied to pattern drawing, a circuit pattern having a large amount ofpattern data can be rapidly and accurately drawn.

However, in the above-mentioned electron beam apparatus, since commonelectrodes are provided for a plurality of electron beams, it can happenthat the spot diameters of the electron beams are slightlydifferentiated, that the beam axes are slightly offset, or that thedeflection angles do not become precisely coincident with each other,due to the mechanical tolerances of the electromagnetic optical systemsfor the respective electron beams. Therefore, in view of the need formaking the electron beam characteristics coincident with each other withhigh precision, there still remains a technical problem to be solved.

FIG. 26 illustrates a problem arising due to fluctuations in the spotdiameters of electron beams. Some defects in a circuit pattern can bedetected with a smaller spot, however, it is often difficult to detectthe same defect with a larger spot. The illustrated waveforms a and brepresent the detected intensity of backscattered or secondary electronsreflected from the sample surface or transmission electrons passingthrough the sample. Although this option is not illustrated in FIG. 26,by providing a detector at the back side of the sample, transmissionelectrons can be captured and converted into an electron signal toobtain one dimensional information relating to the transmission path inaddition to two dimensional information relating to the sample. In thecase of a large spot, signal intensity at defects is so small that it isdifficult to recognize the defects.

FIG. 27 is an explanatory illustration showing a problem arising due tofluctuations of the deflection angle. When the deflection angle becomesexcessive, the electron beam can enter an adjacent irradiation region soas to create an overlapping region presenting a multiple detectionregion. On the other hand, when the deflection angle is too small, anon-irradiated uninspected region can be left between adjacentirradiation regions.

Such a problem may also occur when the electron beam system is used forpattern drawing. In such a case fluctuations in spot diameter maydegrade the precision of patterning. On the other hand, fluctuations indeflection angle may cause degradation of the precision of patterndrawing positions.

Therefore, the present invention proposes an electron beam system thatenables the separate adjustment of the various characteristics of eachindividual electron beam and thus enables the provision of severalelectron beams having uniform precise characteristics.

FIG. 28 shows an embodiment of an electron beam system for implementingthe invention set forth above. As shown in FIG. 28, a plurality ofelectron emitters 521 are formed on a common substrate 520 or separatedsubstrates arranged on a common plane. For each of the individualelectron emitters 521, the system of FIG. 28 includes an extractionelectrode 523 for extracting a charged particle beam 522 from theelectron emitter 521, a converging electrode or coil 524 for convergingthe beam 522 according to a converging ratio corresponding to theelectrode voltage or energization current, a deflection electrode orcoil 525 for deflecting the beam 522 through a deflection anglecorresponding to the electrode voltage or energization current, adetector 529 for detecting secondary or backscattered electrons 527reflected from the surface of the sample 526 or transmission electrons528 passing through the sample 526, and an adjusting means for all orpart of the electrode voltages or energization currents provided for theextraction electrode 523, the converging electrode or coil 524 and thedeflection electrode or coil 525.

In the shown embodiment, the electrode voltages or energization currentsfor each of the charged electron beams can be adjusted independently.For example, by adjusting the electrode voltage of the convergingelectrode 524, the spot diameter of the charged particle beam can beadjusted. On the other hand, by adjusting the electrode voltage of theextraction electrode 523, the beam current is varied to adjust the spotdiameter. As an alternative, by adjusting the electrode voltage of thedeflection electrode 525, the charged particle beam axis can beadjusted.

Therefore, the overall electron beam characteristics can be made uniformwith high accuracy.

A practical embodiment of the electron beam system according to theinvention will be discussed hereinbelow.

FIGS. 29 to 35 show a practical embodiment of an electron beam systemthat is applied as a pattern inspection apparatus.

In FIG. 29, the reference numeral 530 denotes one or more substrates ofa multi-layer structure. The system of FIG. 29 includes a plurality(three are shown in the drawing) of electron emitters 531 to 533 formedof a material, such as or silicon, a metal such as Ta or the like, or acompound such as lanthanum boride or the like. It should be noted herethat the substrate 530 can be a single common substrate for the electronemitters 531 to 533, or as an alternative, can be in the form of anindividual independent substrate for each of the electron emitters 531to 533. As a further alternative, the substrate 530 can be formed bylaminating a plurality of substrates together. In the case of theindividual independent substrates, however, the individual substratesmust be arranged on a common plane and integrated by being fixed to eachother.

Below each of the electron emitters 531 to 533, an extracting electrodeEa_(i). (where i is 531, 532 and 533, and is the same in the following),an anode Eb_(i), a first grounding electrode Ec_(i), a convergingelectrode Ed_(i), a second grounding electrode Ee_(i), a deflectionelectrode Ef_(i) and a detector S_(i) are provided in the stated order.These elements are provided exclusively for corresponding to arespective one of the electron emitters 531 to 533.

Here, discussion will be provided for the major electrodes. Eachextraction electrode Ea_(i) is adapted to extract a charged particlebeam B_(i) having a beam current corresponding to a given electrodevoltage Va_(i). from the electron emitter 531 (or 532 or 533). Theconverging electrode Ed_(i) (converges the electron beam by generatingan electric field having an intensity corresponding to the chargedelectrode voltage Vd_(i). The deflection electrode generates an electricfield corresponding to the charged electrode voltage Vf_(i) forproviding a deflection angle for the electron beam. Other electrodes(anode electrode Eb_(i), first grounding electrode Ec_(i) and secondgrounding electrode Ee_(i)) are adapted to assist in the function of theextraction electrode Ea_(i), or to form an electric field distributionfor converging electrons between the converging electrode. For theseelectrodes, the same electrode potential voltage Vg (groundingpotential) is provided.

The above-mentioned construction merely shows a typical construction innumber of electrodes, layout of electrodes and distribution of chargedvoltages, and should not be regarded as essential for implementing theinvention. Furthermore, although the foregoing example discusseselectrostatic convergence and deflection, the drive functions need notbe energized electrostatically but can alternatively be energizedelectromagnetically. Also, it is possible to use both electrostatic andelectromagnetic energization in combination. However, in the case thatelectromagnetic energization is employed, the converging and deflectionelectrodes should be replaced by converging and deflection coils. Also,the power applied to these elements will be an engergization current.

The detector S_(i), provided for each respective electron beam B_(i) isadapted to catch backscattered or secondary electrons emitted from thesurface of the sample 534, which is an X-ray exposure mask or the like,to mark for aligning the sample 534 to be exposed or a correction unitpattern, which will be discussed later, and to convert such electronsinto an electric signal. The electric signal output from respectivedetectors S_(i) contains information representative of the configurationof a small portion of the electron beam absorber (not shown) on thesample 534, i.e., representative of the circuit pattern in a smallportion of the sample. Accordingly, the two dimensional informationrelating to the sample 534 can be reproduced from all of the electricsignals. Therefore, defective areas (white defects or black defects, forexample) in the fine pattern can be accurately identified.Alternatively, although it is not illustrated, by locating the detectorbehind the sample, transmission electrons can be captured and convertedinto an electron signal to provide one dimensional information of thetransmission path in addition to the two dimensional information of thesample.

The circuits C_(i) for a the respective beams formed by fine processingtechnology on the upper surface of the substrate function as theadjusting means, as set forth above, and the same are adapted togenerate the necessary voltages Va_(i), Vd_(i), Vf_(i) and Vg usingvoltage divider resistors, for example.

FIG. 30 shows a plan view of the circuits C_(i) and the details thereof.The power source voltage V₀ applied to the circuits C_(i) is taken outas Va_(i), Vd_(i) or Vf_(i) through a parallel resistor networkincluding several resistors (R₁, R₂, R₃ and R₄). By selectively cuttingoff the resistor elements, the voltage can be adjusted. Voltageadjustment can also be effective using a series resistor network or acombination of series and parallel resistors. Also, instead of cuttingoff a the selected resistor, an equivalent voltage adjustment can bedone by adding one or more selected resistor. Furthermore, respectiveelements in the resistor network can be formed by transistors. As asuitable device for cutting off and connecting the fine pattern, a maskrepair device disclosed in "Precision Mechanics Paper" (Vol. 53, No. 6,pages 15 to 18) Jun. 5, 1987, Precision Mechanics Association), forexample, in which high luminous FIB (Focused Ion Beam), higher than orequal to 1A/cm² having a beam diameter less than or equal to 0.1 μm, isgenerated for correction (cutting out of black defect or connection bydeposition of the material vapor) of the pattern defect (black or whitedefect) on the photo mask by the FIB.

Referring to FIG. 31, by selectively cutting off respective resistorelements R₁ to R₄ of the circuit C_(i), the electrode voltage Vd_(i) forconverging the electron beam B_(i) can be appropriately adjusted byapplying it to the converging electrode Ed_(i) and varying the voltagedivision ratio of the power source voltage V₀. In this way, theconverging ratio of the electron beam B_(i) converged by the convergingelectrode Ed_(i) can be adjusted so as to adjust the spot diameter.

On the other hand, although it is not illustrated in the drawing, byadjusting the electrode voltage Va_(i) applied to the extractionelectrode Ea_(i), the magnitude of the beam current of the electron beamB_(i) can be adjusted independently since there is a correlation betweenbeam current and spot diameter.

Furthermore, though it is not illustrated, by adjusting the electrodevoltage Vf_(i) supplied to the deflection electrode Ef_(i) the beam axisand the deflection angle of the electron beam B_(i) can be adjusted.

FIG. 31 is an illustration of a connection for adjusting the electrodevoltage Vdzi of a converging electrode Edzi.

As set forth above, since the characteristics of each of the electronbeams can be adjusted independently, the characteristics of the overallelectron beam can be made uniform. Therefore the shown embodiment issuccessful in solving the problem concerning the inconsistency of beamaxes or deflection angles.

Next, a preferred example for detecting fluctuations in thecharacteristics of the electron beam B_(i) will be discussed. FIG. 32(a)is a plan view of a table 535 that is movable in X-Y directions when thesample 534 is mounted thereon. A reference pattern section 536 isfixedly provided at a predetermined position on table 535 so that it canbe placed within the irradiation region of a plurality of electron beamsby shifting the table 535. FIG. 32(b) is a side elevational view whereinthe reference pattern portion 536 is shown as being positioned withinthe irradiation region 537 of the electron beams. A plurality ofelectron beams discharged from an electron beam generator 538 whichincludes a plurality of electron emitters, are irradiated onto thereference pattern portion 536.

In the reference pattern portion 536, a number of precisely designedunit patterns formed from elements having a large atomic weight andcorresponding in number to the number of electron beams are arranged ina regular arrangement. The backscattered or secondary electronsdischarged from respective unit patterns and circumferentialnon-patterned portions, or the transmitted electrons passing through therespective unit patterns and the circumferential non-patterned portionsare detected by the detector Si.

FIG. 33 shows a situation when the electron beam is irradiated on asingle unit pattern and a circumferential non-patterned area. It isassumed that the relative positional relationship between the electronbeam and the unit pattern is shifted from the position A to a position Band then from the position B to a position C by deflecting the beam orby incremental shifting of the table 535. At position A, the entireelectron beam is irradiated on the non-patterned circumferential area.Therefore, the bulk of the transmitted electrons pass through thenon-patterned area. At the position B, the electron beam irradiatesapproximately half of the unit pattern. At this time, the amount oftransmitted electrons is less than that at position A. On the otherhand, at the position C, the electron beam fully irradiates the unitpattern. Therefore, no electrons are transmitted. FIG. 33(b) is a graphillustrating the variation of the beam current representative of thevariation in the transmission of electrons while shifting from theposition A to the position C. As can be seen, the line La shows thevariation of the beam current, in that the beam current is initiallylarge and abruptly decreases across the position B and then becomes 0.FIG. 33(c) is a graph Lb presenting the differentiated value of the lineLa. As can be seen, the differentiated value is 0 at both ends andbecomes maximum at the position B. The width of the differentiated valuecurve, Lb (generally half value width), represents the width of theelectron beam and the spot diameter. Such a measurement is called aknife edge method.

FIG. 34 illustrates another method. In FIG. 34(a), the reference patternis formed from a combination of a light element, having a relativelysmall atomic weight and a heavy element, such as tantalum. The electronbeam is irradiated across the pattern in the same manner. Because of thedifferences in atomic weight, a difference is induced in the generationof backscattered or secondary electrons so that a current variationcurve Lc as shown in FIG. 34(b) is obtained while shifting the beam fromposition A to the position C. Similarly to the knife edge method, thecurve varies swiftly across position B. Then, with the differentiatedvalues, a differentiation curve similar to FIG. 33(c) can be obtainedfor measuring the spot diameter.

The foregoing examples of a practical measurement of the spot diameterare adapted for a single electron beam. The spot diameters of aplurality of electron beams can be measured using the processillustrated in FIG. 35.

FIG. 35(a) illustrates a preferred plane configuration of the unitpattern. Here, by utilizing a triangular unit pattern, the electronbeams are scanned in the three directions F₁ to F₃ respectivelyperpendicular to the three edges of the triangle. By this method, thepure circular spot diameter of the electron beam can be accuratelymeasured. This method also permits a measurement of longer and shorteraxes of an elliptic spot causing astigmatism.

Now, it is assumed that for respective unit patterns P₁ to P₅ forming arandom unit pattern, electron beams B₁ to B₅ respectively havingdifferent spot diameters are irradiated. The scanning direction is setat F₁. The differentiation curves of beam currents of respective unitpatterns are shown in FIG. 35(c). L₁ shows the differentiation curvecorresponding to the electron beam B₁. L₂ shows the differentiationcurve corresponding to the electron beam B₂. Similarly, with respect tothe electron beams B₃ to B₅, the differentiation curves L₃ to L₅ areobtained.

Comparing these curves L₁ to L₅, curve L₅ corresponding to the electronbeam B₃ having the smallest diameter has the minimum width and thehighest peak. Conversely, for curve L₄ corresponding to the electronbeam B₄ having the largest spot diameter, the width attains the maximumvalue and the peak attains the lowest value. The differences between thecurve L₅ corresponding to the minimum diameter and other curves L₁ -L₄correspond to the differences of the spot diameters. Accordingly, byutilizing such differences in the curves, correction values for the spotdiameters for respective electron beams can be derived.

On the other hand, as can be seen from FIG. 35(b), the beam axis (spotcenter) of the electron beam B₄ is slightly offset from the center ofthe oblique edge. Accordingly, by using such offset amount of peakposition, a correction value for the offset of the beam axes for arespective electron beam can be derived.

As the unit pattern, it is possible to use a stencil type pattern withopenings. In such a case, it is desirable to provide current measuringdevices, such as Farady cups, beneath the openings.

Furthermore, as the above-mentioned circuit C_(i), it is also preferableto use a variable power source device, such as a voltage regulatorcircuit, or a programmable power source or the like. In the former case,the correction value for the spot diameter or the beam axis offset isprovided for the reference voltage, and in the latter case, thecorrection value is provided for the program input.

Furthermore, in the case that the subject of correction is of anelectromagnetic type, the above-mentioned circuit C_(i) becomes thecurrent source. In such a case, using resistance division, the currentfrom the current source is appropriately divided. Namely, in the shownembodiment, the diameter and configuration of a respective beam can beindependently measured so that the voltage or current to be applied tothe electrode can be adjusted based on the result thereof, therebymaking it possible to adjust the beam diameters of the electron beams sothat they are substantially equal to each other.

In the above embodiment, a resistor network is used for preciselycontrolling the supplied voltage to the converging electrode, but in thepresent invention, another switching means comprising a plurality oftransistors also can be used as an alternative device instead of theresistor network.

FIG. 44 shows a switching circuit comprising a plurality of transistorsTR1, TR2, TR3 and TR4, which can be used for precisely controlling thevoltage supplied to the converging electrode Edi.

Although in the previous embodiment, the control function can be carriedout by cutting or connecting the resistor or resistors in the resistornetwork, in this transistor embodiment, the control thereof can becarried out by controlling each one of these transistors in an ON/OFFcondition.

A digital-analog converter can be used as a typical type of switchingcircuit and one of the representative circuit constructions therefore isshown in FIG. 45 which is known as a weighing constant current typedigital-analog converter.

In this circuit, the input terminals comprise four bits B1 to B4 andthus the controlling operation can be carried out by applying any one ofthe control signals as 1 or 0, respectively, and accordingly the outputwill be as follows;

    VO=RI(B1/2+B2/2.sup.2 +B3/2.sup.3 +B4/2.sup.4)

Since there is an upper limit in the number of bits in a DAC inpractical use, the range of correction can be limited when theresolution is set excessively high. Therefore, it is desirable tocombine DAC adjustment in combination with resistor adjustment. In thisway, incremental adjustment capability is achieved while maintaining alarge adjustment range.

Further, in the present invention as explained in connection with theabove embodiment, the adjustment of the beam configuration can becarried out on a real-time basis, and thus FIG. 46 shows one example ofa controlling circuit for adjusting beam configuration in real-time.

The circuit of FIG. 46 comprises a signal discriminating portion 46-1which corresponds to the signal discrimination portion 354 as shown inFIG. 20, an analog-digital convertor 46-2 and a digital-analog convertor46-5, a memory means 46-3, a processing means 46-4, and a plurality oflens electrodes 46-7.

In this circuit, the signals output from each of the detectors isdiscriminated by the signal discriminating portion 46-1 and then each ofthe signal wave forms as shown in FIG. 35 is digitized by theanalog-digital convertor 46-2 and stored in the memory means 46-3.

The processing means 46-4 then processes the stored data to producecontrolling data for adjusting the voltage of the conversion lens andsuch controlling data is output to the digital-analog convertor 46-7provided on a substrate from which analog controlling data is output tothe lens electrode.

In the present invention, variations in beam deflection can alsoadjusted utilizing the above circuit.

As can be appreciated, according to the shown embodiment, since thecharacteristics of a plurality of electron beams can be independentlyadjusted, the characteristics of the overall electron beams can beprecisely made uniform so as to avoid fluctuation of the spot diameters,offset of the beam axes, or fluctuation of the deflection angles.

In addition, the shown embodiment can be used to effectively avoidinterference between backscattered electrons from adjacent irradiationregions. Or, as an alternative, the degradation of the S/N ratio due tointerference by reflected beams from adjacent regions can besuccessfully compensated for with the following embodiment.

In order to improve the S/N ratio, another embodiment according to theinvention is constructed as shown in FIG. 42. The FIG. 42 embodiment ofthe pattern inspection apparatus according to the present inventionincludes a plurality of electron emitters arranged in a parallelrelationship and in a matrix. Each of the emitters is provided with afine electrode with a sharply headed tip end, a gate surrounding the tipend of the fine electrode, a converging electrode, a deflectionelectrode and a detector. Electron beams are simultaneously irradiatedon the surface of the sample from the parallel electron emitters. Thebackscattered or secondary electrons from the surface of the sample arecaught by a detecting surface of each detector. Based on the amount ofbackscattered or secondary electrons, the condition of the surface ofthe sample is determined. A mask having an opening with a predeterminedinternal diameter is arranged so that the center of the opening isaligned with the axis of the electron beam, at a position between thesurface of the sample and the detecting surface of the detector which isdetermined based on the distance from the surface of the sample to thedetecting surface and the size of the detecting surface.

The practical construction of the FIG. 42 embodiment will be discussedwith reference to FIG. 35.

In FIG. 42(a), an electron beam 610 is emitted from one of a pluralityof electron emitters and an electron beam 611 is emitted from anadjacent electron emitter. The electron beams 610 and 611 aresimultaneously irradiated onto two points P₁ and P₂ which are spacedapart by a distance L. The electrons (or secondary electron) are emittedfrom the points P₁ or P₂.

The reference numerals 613 and 614 denote detectors provided in thevicinity of the outlets of the electron beams 610 and 611. Thesedetectors 613 and 614 catch the backscattered or secondary electrons ofthe corresponding electron beam on a surface having a given area so asto output an electric signal proportional to the amount of electronscaught.

Between the detectors 613 and 614 and the sample 612, a mask 615 withopenings is provided. The mask 615 is formed with a number of circularopenings (for example, nine openings 615a to 615i as shown)corresponding to the number of electron beams. The center of eachcircular opening (for example, openings 615a and 615b) is preciselyaligned with the axis of the corresponding electron beams (for example610 and 611).

The preferred position of the mask 615 with the openings therein isderived through the following manner. Assuming that the distance fromthe surface of the sample 612 to the detectors 613 and 614 is h, thedistance from the surface of the sample 612 to the mask 615 is y, theradius (corresponding to the size of the detecting surface) of thedetecting surface of the detectors 613 and 614 is a, the radius of theopenings 615a to 615i of the mask is x, the distance between theirradiating points P₁ and P₂ of the electron beams is L, then theposition of the mask 615 is selected so that either x/a or y/h is in therange of from 1.0 to 0.5 and a/L is in the range of from 0 to 0.5 (referto FIG. 42C).

For example, when the distance between the detectors 613 and 614 issubstantially 0, a/L becomes 0.5. Therefore, in such a case, thepreferred position of the mask 615 is determined so that x/a or y/h is0.5. Therefore, the position of the mask 615 is selected so as to placethe circular opening having a radius x, which is approximately one halfof the radius of the detecting surface, at approximately an intermediateposition (y/h=0.5) of the distance between the surface of the sample 612and the detectors 613 and 614 (y/h=0.5).

It should be appreciated that FIG. 42(a) shows an example for the casewhere a/L m x/a×y/h×0.5. In this example, the backscattered electrons616 backscattered from the point P₁ toward the detector 613 and thebackscattered electrons 617 backscattered from the point P₂ toward thedetector 614 can pass through the circular openings 615a and 615b.However, backscattered electrons from an adjacent irradiation region,such as the backscattered electrons 618 backscattered from the point P₁toward the detector 614, are blocked from passing through opening 615bby the solid portions of mask 615. Accordingly, with the shownembodiment, inpurgement of backscattered electrons from an adjacentirradiation region to a given detector can be positively eliminated toenhance the accuracy of detection.

Next, a fifth embodiment of the present invention will be discussed. Thefifth embodiment is illustrated in FIG. 36, in which, the shownembodiment of the pattern inspection apparatus comprises a plurality ofelectron emitters arranged in a matrix fashion. Each of the electronemitters includes a fine electrode with a sharp headed tip end and agate surrounding the tip end of the fine electrode. A convergingelectrode, a deflection electrode and a detector is provided for each ofthe electron emitters. Parallel electron beams are emitted from theelectron emitters simultaneously so as to irradiate the surface of thesample. Backscattered or secondary electrons are caught by the detectingsurface of the detectors provided for each of the electron beams. Basedon the amount of the backscattered or secondary electrons captured bythe detectors, the condition of the surface of the sample is determined.A plurality of thin tubes having a predetermined length are provided inan orientation such that the longitudinal axes thereof are in parallelalignment with the axes of the electron beams.

In a practical construction, as shown in FIG. 36, a bunch of thin tubesis arranged in the proximity of the detectors (only detectors 620 and621 are shown in the drawing). As said thin tube, a lead glass tube of20 μmφ, which is used in an electron multiplier for MPC (microchannelplate) or so forth, is available. In the electron multiplier, the tubeis slightly inclined relative to the axis of the electron beam so thatthe electrons collide on the inner periphery of the tube to provideenergy corresponding to the potential of the inner wall for thebackscattered electrons. Conversely, in the shown embodiment, the tubesare provided precisely in alignment with the axis of the electron beamand no potential is provided for the inner wall.

With such an arrangement, the electron beams (typically 623, 624) can beirradiated on the sample 625 without any interference. On the otherhand, only those backscattered electrons having a reflection anglesmaller than or equal to a given angle are permitted to pass through thetube. Therefore, backscattered electrons from an adjacent irradiationregion (which has too large a reflection angle) will not enter a giventube. Therefore, interference by backscattered electrons from anadjacent irradiation region can be positively prevented. As can beappreciated, the reflection angular range to permit passing through thetubes can be easily adjusted by selecting the diameter and length of thetubes.

FIG. 37 shows a sixth embodiment of the invention, in which embodimentthe pattern inspection apparatus comprises a plurality of electronemitters arranged in a matrix fashion. Each of the electron emittersincludes a fine electrode with sharp headed tip end and a gatesurrounding the tip end of the fine electrode. A converging electrode, adeflection electrode and a detector are provided for each of theelectron emitters. Parallel electron beams are emitted from the electronemitters simultaneously and irradiate the surface of the sample. Thebackscattered or secondary electrons 634 from each beam 635 are caughtby the detecting surface of the detectors 632. Based on the amount ofthe backscattered or secondary electrons captured by the detectors, thecondition of the surface of the sample is determined. The detectors arearranged between the converging and deflecting electrodes and theelectron emitter.

As shown in FIG. 37, the detector 632 is positioned between the electronlens system comprising the converging electrode 630 or the deflectionelectrode 631 and the electron emitter.

With such construction, the backscattered electrons 634 from the focuspoint of the electron lens system are deflected so as to besubstantially parallel to the electron beam 635 applying the principleof a convex lens and thus can easily reach the detector 632. Conversely,the backscattered electrons 636 from the focus point of an adjacentelectron lens system intersect with the axis of the electron beam 635and are unable to reach the detector 632. Therefore, with the shownarrangement, the precision in detection can be enhanced.

FIGS. 38 to 41 show a seventh embodiment of the invention in which thepattern inspection apparatus comprises a plurality of electron emittersarranged in a matrix fashion. Each of the electron emitters includes afine electrode with sharp headed tip end and a gate surrounding the tipend of the fine electrode. A converging electrode, a deflectionelectrode and a detector are provided for each of the electron emitters.Parallel electron beams are emitted from the electron emitterssimultaneously so as to irradiate the surface of the sample. Thebackscattered or secondary electrons are captured by the detectingsurface of the detector provided for each electron beam. Based on theamount of the backscattered or secondary electrons captured by thedetectors, the condition of the surface of the sample is determined. Thedetected value of a given detector is processed by subtracting a valuederived by multiplying respective signals of a plurality of surroundingdetectors by a predetermined coefficient.

As shown in FIG. 38, the reference numerals 651 to 659 denote respectivedetectors provided for corresponding electron emitters arranged in amatrix array. The detectors 651 to 659 are arranged in regularincremental intervals. The detection signals PS₆₅₁ to PS₆₅₉ are providedto the signal processing section 660. The signal processing section 660effects a predetermined signal processing operation to output correcteddetection signals SS₆₅₁ to SS₆₅₉.

FIG. 39 is an illustration showing an embodiment of the patterninspection apparatus according to the invention.

Here, considering two adjacent detectors (for example, detectors 651 and652 of FIG. 38), one of the detectors (for example 652) catchesbackscattered electrons 662 of the electron beam 661 from its ownelectron beam generating source and also catches backscattered electrons664 of the electron beam 663 from the electron beam generating sourcecorresponding to the adjacent detector 651. Then, by the presence of thebackscattered electrons 664, the S/N ratio of the detector 652 isdegraded. The S/N ratio of the detector 652 is further degraded by theinfluence of a plurality of adjacent electron beams.

The detection signals PS₆₅₁ and PS₆₅₂ the detectors 651 and 652 areexpressed by the following equations:

    PS.sub.651 =SS.sub.651 +N.sub.652                          (1)

    PS.sub.652 =SS.sub.652 +N.sub.651                          (2)

where SS₆₅₁ is a value corresponding to the amount of backscatteredelectrons 665 of the electron beam 663, and SS₆₅₂ is a valuecorresponding to the amount of backscattered electrons 662 of theelectron beam 661, these values being the true values to be detected.N₆₅₁, is a value corresponding to the amount of backscattered electrons664 of the electron beam 663 and N₆₅₁ corresponds to the amount ofelectrons (not shown) of the electron beam 661, and these values serveto cause degradation of the S/N ratio by being superimposed on the truevalues.

N₆₅₁ is proportional to the amount SS₆₅₁ of the backscattered electrons665, as expressed by the following equation (3), and N₆₅₂ isproportional to the amount SS₆₅₂ of the backscattered electrons 662, asexpressed by the following equation (4). Namely, the values N₆₅₁ andN₆₅₂ will increase according to an increase in the amount ofbackscattered electrons 665 and 662.

    N.sub.651 k·SS.sub.651                            (3)

    N.sub.652 k·SS.sub.652                            (4)

k in the foregoing equations (3) and (4) is a coefficient between N₆₅₁and S₆₅₁ and between N₆₅₂ and SS₆₅₂. The amount of this coefficient k isdetermined according to the positional relationship between thedetectors 651 and 652. For instance, when two detectors 651 and 652 areclose together, k becomes large, and when these detectors are far apart,k becomes smaller. It should be noted that the coefficient between N₆₅₁and SS₆₅₁ is not the same as that between N₆₅₂ and SS₆₅₂, in a strictsense, because of tolerances of the detectors. However, the use of atypical coefficient k derived on the basis of average design data whichtakes into consideration the distance between the detectors and the sizeof the detecting surfaces will not create a problem.

Using the foregoing equations (1) through (4), the following equations(5) and (6) can be established.

    PS.sub.651 =(a-k.sup.2)·SS.sub.651 +k·PS.sub.652(5)

    PS.sub.652 =(a-k.sup.2)·SS.sub.651 +k·PS.sub.652(6)

And since k is less than 1,

    PS.sub.651 ˜SS.sub.651 +k·PS.sub.652 ΔSS.sub.651 ˜PS.sub.651 -k·PS.sub.652                  (7)

    PS.sub.652 ˜SS652+k·PS.sub.651 ΔSS.sub.652 -PS.sub.652 -k·PS.sub.651                                    (8)

Accordingly, in order to obtain the true signal SS₆₅₁ by removing thenoise component N₆₅₂ from the detection signal PS₆₅₁ of the detector651, the value is derived by multiplying the detection signal valuePS₆₅₂ of the detector 652 by the coefficient k from the detection signalPS₆₅₁ of the detector 651. Similarly, in order to obtain the true signalSS₆₅₂ by removing the noise component N₆₅₁, from the detection signalPS₆₅₂ of the detector 652, the value is derived by multiplying thedetection signal value PS₆₅₁ of the detector 651 by the coefficient kfrom the detection signal PS₆₅₂ of the detector 652.

FIG. 40 is a block diagram showing a circuit for performing theforegoing subtraction process. In this example, as shown in FIG. 40(a),the circuit comprises two subtractors 670 and 671 and two multipliers672 and 673. The multiplier 673 multiplies the detection signal PSA by acoefficient kA. The subtractor 671 subtracts the product obtained by themultiplier 673 from the detection signal PSB to derive the truedetection signal SSB. Similarly, the multiplier 672 multiplies thedetection signal PSB by a coefficient kB. The subtractor 670 subtractsthe product obtained by the multiplier 672 from the detection signal PSAto derive the true detection signal SSA. In the preferred constructionas shown in FIG. 40b, the subtractors are formed by operationalamplifiers 680 and 681. The inverting inputs (-) of the operationalamplifiers 680 and 681 are input via resistors R_(A) and R_(B) atlocations between respective inverting inputs (-) and the detectionsignal input terminals 682, 683 variable resistors VR_(A) and VR_(B) maybe used to interconnect amplifiers 680 and 681 and the setting ofresistors VR_(A) and VR_(B) determines the coefficients value of thek_(A) and K_(B).

In the foregoing example, discussion has been provided for the casewhere two detection signals are processed. However, in the practicalimplementation of pattern inspection apparatus according to the presentinvention, a greater number of detection signals must be processed.

For example, FIG. 38 shows an example in which 9 detectors 651 to 659are provided. In this example, several groups are formed with thedetectors having a positional relationship so as to have equalcoefficients with respect to the specific detector (for example,detector 655 of FIG. 38) for which a true detection signal is to beobtained. In the shown example, the detectors 652, 654. 656 and 658 formone group that will hereafter be referred to as group a, and thedetectors 651, 653, 657 and 659 form another group hereafter referred toas group B. The detection signals of the detectors in each group aresummed. The sum thus calculated is multiplied with a coefficient whichis common for the detectors in the group. Namely, in the shown case, thesum of the detection signals in the group a is multiplied by thecoefficient kα. The product thus derived is subtracted from the detectorsignal PS655 of the detector 655 to derive the true detector signalvalue. This process is expressed by the following equation (9):

    SS.sub.655 =PS.sub.655 -kα, εPSα-kβ·εPSβ     (9)

where

εPSα=PSS₆₅₂ +PS₆₅₄ +PS₆₅₆ +PS₆₅₈

εPSβ=PS₆₅₁ +PS₆₅₃ +PS₆₅₇ +PS₆₅₉

In the foregoing equation (9), the common equations kα and kβ are usedfor the detector signals of the detectors positioned respectively atequal distance from the specific detector for which a true detectionsignal SS₆₅₅ is to be derived.

If different coefficients are used, the following equation (10) isestablished: ##EQU1##

The suffix, such as 651-655, represents the coefficient between thedetectors 651 and 655.

Further discussion will be provided concerning the enhancement of theS/N ratio with reference to FIG. 41. The detection signal in the case ofno pattern, at which the backscattered electrons from the irradiatingregion are at a minimum, is illustrated by a single bar graph 690.Conversely, the detection signal in the case where a of thebackscattered electrons is large, is illustrated by a double line graph691. In addition, the hatched areas of the bar graph represent the truedetection signal values which are respectively expressed as S_(OFF)(pattern absent) and S/N (pattern present).

Now, consideration is provided for the case where the pattern ispresent. In this case, assuming that the backscattered electrons of theadjacent electron beam are at a zero value, the signal S_(ON)corresponding to the hatched portion of the bar graph 691 (or 692),namely the true detection signal, can be obtained when the backscatteredelectrons of the adjacent electron beam are included in the detectionsignal as a noise component. In this case, when all of the adjacentirradiation regions have patterns, the maximum noise component (N_(max))should be superimposed on the true detection signal. On the other hand,when all of the adjacent irradiating regions have no patterns, theminimum noise component (N_(min)) is superimposed on the true detectionsignal. The following equation expresses the S/N ratio of the case ofFIG. 41.

    S/N=(S.sub.ON -S.sub.OFF)/(S.sub.ON +"N"-S.sub.ON)         (11)

In the foregoing equation "N" is to be replaced for N_(max) to N_(min).The greater N value will degrade the S/N ratio. Therefore, by setting anoptimum coefficient k (it is desirable to vary such coefficientdepending upon the presence and absence of the pattern) with respect tothe adjacent beams to subtract the product (k·S_(ON)) of the coefficientk and the detection signal value of the adjacent beam from the detectionsignal value to compensate for the noise component, the S/N ratio can beenhanced.

It should be noted that the electron beam scanning device is applicablenot only to electron beam drawing systems and electron beam inspectionsystems but also to plane display systems or a wide variety of electronbeam utilizing products.

With the foregoing embodiment, the interference of backscatteredelectrons of adjacent beams can be positively prevented or successfullycompensated for to obtain an enhanced S/N ratio.

Although the invention has been illustrated and described with respectto an exemplary embodiment thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be understood as limited to thespecific embodiment set out about but includes all possible embodimentsthat are within the scope encompassed and equivalents thereof withrespect to the features set out in the appended claims.

Another embodiment of the present invention is described herebelow.

In the electron beam apparatus according to this embodiment, a pluralityof electron emitters are formed on an individual substrate disposed one-or two- dimensionally on the same substrate or in the same plane. Eachof the electron emitters is provided with extraction electrode toextract from the electron emitter a charge particle beam having a beamcurrent corresponding to the electrode voltage, a converging electrodeto converge the charged particle beam at a convergence ratiocorresponding to the electrode voltage or energization current, adeflection electrode to deflect the charged particle beam at adeflection angle corresponding to the electrode voltage or energizationcurrent, a beam shaping electrode to correct misalignment between theaxis of the charged particle beam and the central axis of the convergingelectrode to shape the charged particle beams and a detector to detectsecondary or backscattered electron from the surface of a sample exposedto the converged and deflected charged particle beam or electrons whichhave been transmitted through the sample. Also there is provided anadjustment mechanism to adjust the electrode voltage applied to theextraction electrode, the converging electrode, the deflection electrodeand the beam shaping electrode.

In this embodiment, the beam shaping electrode should preferably be anelectrostatic eight-pole electrode having at least one step and which isbuilt into the grounded electrode of the electrostatic lens for agreater effect.

In the foregoing embodiment, the electrode voltages to energizationcurrents for each charged particle beam are individually adjusted. Forexample, the electrode voltages of the converging electrode and of theextraction electrode are adjusted individually to change the beamcurrent, thereby changing the spot diameter. The electrode voltage ofthe deflection electrode is then adjusted to change the axis of thecharged particle beam.

Also, the spot of the beam is ideally shaped by the beam shapingelectrode.

Thus, the characteristics of each charged particle beam are uniformlyaccurate.

This embodiment of the present invention will be discussed in furtherdetail.

In an ordinary scanning electron microscope or electron beam exposuresystem, an eight-pole electromagnetic coil or electromagnet called a"stigmator" is used to correct the beam shape.

It is possible also in the above-mentioned embodiment for the beam shapeto be distorted by manufacturing errors or the like.

A larger number of electron emitters than is required by the electronbeam gun tube may provided so that they are selectable at any timebecause of the life of each emitter. However, this arrangement willpossibly cause the axial misalignment between the electron emitters andthe electron beam gun tube which will also cause the beam shape todistort.

According to this embodiment, a plurality of electrostatic eight-poleelectrodes is disposed in each electron beam optical system to correctthe misalignment between the central axis of the electrostatic lens andthe beam axis and shape the beam into an ideal circular shape.

The principle of this embodiment is explained herebelow with referenceto FIGS. 47 to 52.

In FIG. 49, the illustration includes an electron emitter 751, anacceleration electrode 752, a two-step eight-pole electrostaticelectrode 753, an electrostatic Einzel lens 754 and a sample 755.

By applying a voltage to the electrostatic eight-pole electrode 753 asshown in FIG. 47(a), a deflection field can be produced, and bydistributing the voltage as shown in FIG. 47(b), the stigmator functionsas correct the beam shape.

More particularly, by applying each electrode with two superposedvoltages, it is possible to correct both the axial misalignment andstigmatism, and when it is desired to simultaneously translate the beamaxis and change the angle, it suffices to provide a further plurality ofelectrostatic eight-pole electrodes.

Each pole 802 of the electrostatic eight-pole electrodes in eachelectron beam optical system can be applied with an appropriate voltagethrough a correction circuit elaborately built into the electron beamgenerator similarly to the aforementioned embodiment.

In this case, the pattern shown in FIG. 35 is used. By scanning theelectron beam in the vertical, horizontal and oblique directionsindicated by F₁ to F₃ in FIG. 35, a two-dimensional spot shape can bedetermined in addition to the spot diameter of each electron beam.Therefore, it suffices to adjust the voltage applied to each pole 802 ofthe electrostatic eight-pole electrodes in each electron beam opticalsystem based on the spot shape.

Taking into consideration the need for matching with conventional microprocessing techniques, the electrostatic eight-pole electrodes can bemade by forming first a thin electrically conductive film on aninsulation substrate 801 and patterning such film by a process similarto that used for producing the wiring of an ordinary IC (integratedcircuit) as shown in FIG. 44.

For correction of the misalignment between the electron beam axis andelectrostatic lens axis, it is necessary to locate the electrostaticeight-pole electrode at the electron emitter rather than at theelectrostatic lens as shown in FIG. 49.

Also, in case the correction of axial misalignment is not so essential,namely, when it is the main purpose to shape the spot, one electrode ofthe Einzel lens 754 may be divided into 8 pieces and a stigmator voltagemay be applied to each of the pieces as shown in FIG. 50, since theelectrostatic eight-pole electrode 753 and the Einzel lens 754 can beused for the same purpose.

Normally, a voltage is applied while the opposite sides of theelectrodes are connected to a ground potential.

The thickness of each electrode of the electrostatic lens has aninfluence on the convergence effect, and the central electrode has thelargest such influence. The greater the electrode thickness, the largerthe convergence becomes. As will be described below, when the spotshaping capability is low, it is preferable for the electrostaticeight-pole electrode to be grounded at both sides of the centralelectrode as shown in FIG. 50.

The capability of deflection, that is, the capability of deflecting theelectron beam as a function of the applied voltage, depends upon thelength of the deflection electrode in the direction of the beam axis.The greater the length, the higher the capability of deflection becomes.

This is also true for the stigmator's capability of beam shaping. With athin film as shown in FIG. 50, the capabilities of beam deflection andshaping are relatively low.

How thick the electrode should be depends upon the acceleration energyof electron beam, the necessary extent of correction of beam axialmisalignment or the extent of correction of beam shape. However, if itis necessary to increase the capability of beam deflection and shaping,the forming of a rather thick electrically conductive film in theprocess of elaborately forming electron beam optical system takes a longtime, which is not practical.

To avoid the foregoing difficulties, first, an electrically conductivematerial 804 is deposited obliquely from above onto the insulationsubstrate with an opening as shown in FIG. 51(a), and then theinsulation substrate is rotated to from an electrode pattern.

Next, the electrode pattern 805 thus formed is wired (803) at the topthereof as shown in FIG. 51(b). The inner wall of the opening is cut foreach electrode using a converged ion beam FIB, thereby permittingformation of electrodes having length in the beam-axial direction.

Also in this case, the electrically conductive material 804 depositedaround the opening in the insulation substrate may be a material whichhas relatively high resistivity and the wiring 803 may be a materialhaving a low resistivity. Thus, the connection between the electrodepattern and wiring takes on a wiring potential and a small current flowsbetween the adjoining connections. That is, a potential differenceoccurs between them. With this arrangement, necessary deflection andshaping fields can be produced inside the opening of the insulationsubstrate without the necessity of electrically isolating the electrodesfrom each other.

The correction circuit may be an ordinary electronic circuit externallyprovided independently of the electron beam generator as in theaforementioned embodiment. However, since the electron beam generator ismade by building an electron emitter, convergence electrode, deflectionelectrode, etc., in a silicon substrate using micro processingtechniques, the correction circuit can be built as a micro IC in anysubstrate. In this case, the correction circuit may include, forexample, a resistance division circuit, a digital/analog conversioncircuit, a voltage regulation circuit, etc.

Therefore, in this embodiment, beam spot shape distortion in theelectron beam optical system is inhibited, thus providing improvedaccuracy in detecting defect, in the wafer mask or exposure with ahigher resolution and speed.

The number of electrodes, electrode disposition and voltage distributionin this embodiment are typical, but the present invention is not limitedonly to this arrangement.

In the foregoing description, an embodiment has been described whichadopts the system of electrostatic convergence and deflection. However,the system may be an electromagnetic convergence and deflection or amixed system of electrostatic and electromagnetic convergence anddeflection. However, in a case where an electrode is replaced with acoil, the electrode voltage applied to the electrode becomes theenergization current.

In this embodiment, the electrode voltages or energization currents canbe adjusted individually for each of the plurality of charged particlebeams and the beam spot can be ideally shaped by beam shaping and madeuniform with high accuracy.

Therefore, it is possible to minimize the spot diameter difference, beamaxial alignment, fluctuation of deflection angle, distortion of spotshape, etc.

We claim:
 1. A pattern inspection apparatus, comprising:a plurality ofelectron emitters, formed on an individual substrate disposed one- ortwo-dimentionally on a same substrate or in a same plane, there beingprovided for each of said electron emitters:an extraction electrodewhich extracts from said electron emitter a charge particle beam havinga beam current corresponding to an electrode voltage, with respect toeach one of said plurality of electron emitters; a converging electrodefor converging said charged particle beam at a convergence ratiocorresponding to the electrode voltage or energization current; adeflection electrode for deflecting said charged particle beam at adeflection angle corresponding to said electrode voltage or energizationcurrent; a beam shaping electrode for correcting the misalignmentbetween the axis of said charged particle beam and the central axis ofsaid converging electrode to shape said charged particle beam; and adetector operable to detect all of or part of respective secondary orbackscattered electrons from the surface of an inspection sample exposedto the converged and deflected charged particle beam or transmittedelectrons passing through said inspection sample; wherein said apparatusis further characterized in that said apparatus being also provided witha means for adjusting said electrode voltage applied to said extractionelectrode, converging electrode, deflection electrode and beam shapingelectrode.
 2. A pattern inspection apparatus as set forth in claim 1,wherein said beam shaping electrode is an electrostatic eight-poleelectrode of more than at least one step.
 3. A pattern inspectionapparatus as set forth in claim 2, where said beam shaping electrode isprovided in a grounded electrode of said electrostatic lens.
 4. Apattern inspection apparatus as set forth in claim 1, wherein saidadjustment means is provided as an IC or resistor network in a substratewhere said electron emitter is formed.
 5. A pattern inspection apparatusas set forth in claim 1, further comprising a means for detecting eachbeam shape based on a preset reference pattern to calculate a correctionamount of the voltage applied to said convergence electrode, deflectionelectrode and beam shaping electrode.
 6. A pattern inspection apparatuscomprising:a plurality of electron emitters arranged on a commonsubstrate or on a plurality of individual substrates arranged on thesame plane, each said electron emitter comprising (a) an extractingelectrode component for extracting a charged particle beam having a beamcurrent corresponding to an electrode voltage from said electronemitter; and (b) a converging component in the form of an electrode orcoil providing a converging ratio for said charged particle beamcorresponding to an electrode voltage or an energization current; adetector operable to detect all of or part of respective secondary orbackscattered electrons from the surface of an inspection sample exposedto the converged and deflected charged particle beam or transmittedelectrons passing through said inspection sample; and an adjustment unitadjusting all of or part of the respective electrode voltages orenergization voltages applied to said extracting and convergingcomponents by selectively disconnecting or connecting each saidcomponent in the resistor network or the wiring connected to thecomponent, said unit being provided in a substrate where a said electronemitter is formed.
 7. A pattern inspection apparatus as set forth inclaim 6, wherein each said electron emitter includes a deflectioncomponent in the form of an electrode or coil providing a deflectionangle to said charged particle beam corresponding to an electrodevoltage or an energization current, said adjustment unit adjusting allof or part of the respective electrode voltages or energization voltagesapplied to said deflection components by selectively disconnecting orconnecting each said deflection component in the resistor network or thewiring connected to the deflection component.